Brains will be obtained at autopsy from three mental retardates with minimal neurological complications and from six normal humans. Both groups will be matched as closely as possible, and cause of death will be non-neurological. Measures will be taken from an association area (mid-temporal gyrus), a primary sensory area (post-central gyrus) and a primary motor area (pre-central gyrus). The measures to be made are size of cell body in Nissl stained slides and lengths and numbers of dendrite segments and numbers and locations of branch points of the dendritic trees of Golgi-Cox stained neurons. These measures will be taken with the aid of a computerized scanner recently developed in our laboratory. Data from the brains of retardates and from the brains of the matched normal controls will be compared using multivariate statistics to determine whether there are statistically significant differences between these two samples with respect to the measures obtained.